Typical surgical tourniquet systems of the prior art include a tourniquet cuff which encircles the limb of a surgical patient, and a tourniquet instrument which is releasably connected to the tourniquet cuff through a length of tubing, establishing a sealed gas passageway between the cuff and instrument. Tourniquet cuffs typically include an inflatable portion, which encircles the limb of a patient at a desired location, and is connected through a cuff port to a tourniquet instrument through one or more sections of tubing.
The tourniquet instrument contains a pressurized gas source which is used to inflate and regulate the pressure in the tourniquet cuff above a minimum pressure required to stop arterial blood flow distal to the cuff, for a duration suitably long for the performance of a surgical procedure. Many types of surgical tourniquet systems have been described in the prior art, such as those described by McEwen in U.S. Pat. Nos. 4,469,099, 4,479,494, 5,439,477 and McEwen and Jameson in U.S. Pat. Nos. 5,556,415 and 5,855,589.
A number of different types of disposable tourniquet cuffs are known in the prior art. These cuffs are intended to be used within sterile surgical fields, and are typically sterilized at the time of manufacture. Examples of multi-layer disposable cuffs in the prior art are described by Robinette-Lehman in U.S. Pat. No. 4,635,635, and in commercial products manufactured in accordance with its teachings (‘Banana Cuff’ sterile disposable tourniquet cuffs, Zimmer Arthroscopy Systems, Englewood Colo.), and by Guzman et al. in U.S. Pat. No. 6,506,206, and in commercial products manufactured with its teachings (‘Comfortorm™ Disposable Gel Cuff’, DePuy Orthopaedics Inc., Warsaw Ind.). A two-layer disposable cuff of the prior art is described by Spence in U.S. Pat. No. 5,733,304. Disposable cuffs of the prior art tend to be constructed using exotic materials, such as gel layers, and large amounts of of materials, such as multi-layer cloth/thermoplastic laminates, which are expensive . Also, the use of these materials in prior-art cuffs has tended to result in a greater overall cuff thickness and stiffness, making the cuffs difficult to apply consistently. Thicker and stiffer cuffs of the prior art may also degrade performance after cuff application so that higher tourniquet pressures may be required to reliably occlude blood flow; this is undesirable because higher tourniquet pressures are associated in the surgical literature with a higher risk of patient injury.
Typical tourniquet cuffs of the prior art include a sealed bladder which encircles the limb and which communicates pneumatically with a connected tourniquet instrument through one or more gas passageways, a stiffener to help direct the expansion of the cuff bladder radially inwards towards the limb and to help prevent twisting of the cuff and rolling of the cuff along the limb, and one or more fasteners for securing the cuff around the limb.
In order to facilitate the attachment of fasteners and the establishment of gas passageways to the cuff, the assembly process is completed in several labor-intensive operations, some of which require a high level of skill. These operations can include sewing fastener materials to the outer cuff layer, adding a structural reinforcing patch to the outer layer, sealing the port to the bladder layer, and sealing the bladder perimeter.
Cuff layers consisting of compatible thermoplastic polymeric materials are typically joined together using a radio frequency (RF) welding process, which uses a combination of heat and pressure to cause compatible polymers to flow together by molecular diffusion. Welding operations to make cuffs of the prior art are typically completed in multiple steps, each of which typically requires operator intervention. Cuff layers are positioned in a bottom die plate, and then engaged against a top die plate by a pneumatic press. A typical tourniquet cuff of the prior art requires at least two welding operations to form the bladder.
The bladder is typically formed from two separate sheets of thermoplastic coated material and sealed around a perimeter using an RF welding process. The gas passageways into the bladder are formed through single or multiple port flanges, which are sealed through the bladder using the RF welding process. The port provides a reinforced structure which is attached to tubing that extends outside the sterile surgical field for connection to a tourniquet instrument. The port flange is sealed to a single side of the bladder in a separate operation, to prevent the opposite bladder surface from bonding at the port location. The bladder seal is usually completed in a single operation, after the attachment of one or more ports, and lies around the perimeter of the cuff close to the edges.
Tourniquet cuffs of the prior art typically include a thermoplastic stiffener element, which helps direct the expansion of the cuff bladder radially inward towards the limb when pressurized, and helps reduce the tendency of the cuff to twist when pressurized and to roll along a tapered limb. The absence of an internal stiffening element leads to a reduction of the efficient application of pressure to the limb, and thus leads to an increase in the level of pressure required to stop blood flow past the cuff and into the limb. Also, the absence of a stiffening element would lead to additional stresses in the outer cuff surface due to less constrained bladder expansion. To help direct expansion of the cuff bladder, tourniquet cuffs of the prior art contain a stiffener element in one of several configurations. The first, most widely used type of stiffener configuration contains a non-inflating sheath which houses the stiffener outside the inflatable bladder (as in Zimmer ATS sterile disposable tourniquet cuffs distributed by Zimmer Inc., Dover Ohio). This method of constraining the stiffener facilitates the inward expansion of the cuff into the soft tissues of the limb encircled by the cuff when the cuff is pressurized, and provides resistance to twisting and rolling. It also results in a cuff that is thinner than other pre-art cuffs, which reduces wrinkling on the inner surface of the cuff caused by differences of circumference between the inner and outer cuff surfaces.
A second type of stiffener configuration in cuffs of the prior art involves increasing the thickness and rigidity of the outer cuff material layer, to obtain a stiffening function from the outer layer in a two-layer cuff design (as described by Eaton in U.S. Pat. No. 5,413,582, and in cuffs distributed by Oak Medical, Briggs, North Lincs, UK,). The outer layer of these prior-art cuffs serves both as a stiffener and as one side of the inflatable bladder. The thick outer layer extends to all the cuff edges, and includes an area for sealing the inner layer to the thick outer layer to form the bladder, resulting in the bladder always having a width that is less than the width of the stiffener; this is undesirable because cuffs having narrower bladder widths require higher tourniquet pressures to stop blood flow, and higher tourniquet cuff pressures are associated with a higher risk of patient injury. Also, this second type of stiffener configuration in cuffs of the prior art, in which the stiffener forms part of the inflatable bladder, greatly limits the extent to which the cuff can expand inwardly into soft tissue when the cuff is pressurized; this limitation increases the pressure required to stop or occlude blood flow in the encircled limb, especially in obese patients and patients having large amounts of soft tissue. Further, the thick and stiff edges formed at the side edges of these prior-art cuffs may have a tendency to buckle towards the limb, leading to a potential soft-tissue hazard.
A third stiffener configuration in tourniquet cuffs of the prior art consists of an unsecured stiffener placed within the inflatable bladder (for example, as described by Spence in U.S. Pat. No. 5,733,304, by Goldstein et al. in U.S. Pat. No. 5,411,518, and as seen in ‘Color Cuff II’ sterile disposable tourniquet cuffs distributed by InstruMed Inc., Bothell Wash.). In this configuration, the stiffener is unsecured within the bladder and does not constrain the expansion of the outer cuff surface. This reduces the effectiveness of the stiffener in directing cuff pressure toward the encircled limb across the width of the cuff, and it reduces the extent to which the cuff can expand inwardly when pressurized, thereby making its performance more sensitive to variations in application technique and thereby leading to the possible need for higher tourniquet pressures to stop blood flow past the cuff and into the limb, particularly in patients having large amounts of soft tissue and in patients with poor muscle tone. Further, an unsecured stiffener within the cuff bladder is not as effective as a secured stiffener in helping to prevent the cuff from twisting or rolling axially along the limb. In addition, in order to reduce the limitations of performance that are inherent in a cuff having an unsecured stiffener within the inflatable bladder, the width of the stiffener in prior art cuffs has been increased to be as close as possible to the bladder width, which impairs cuff performance and which requires precise alignment of the stiffener during manufacture.
Cuffs of the prior art typically employ hook and loop type fastener elements, which are attached to the outer layer of the cuff. The most common configuration consists of a hook-type strap which wraps around and engages with a loop-type material, which is contained by the outer surface of the cuff.
In general, it is desirable to construct the thinnest tourniquet cuff possible for a given application, to reduce wrinkles on the inner cuff surface and to allow the user to apply the cuff snugly to the limb. Drawbacks associated with thicker, more rigid cuff materials are discussed above, and many are caused by prior art attempts to combine several cuff elements into a single composite material. This often results in an increase in thickness and overall rigidity, and a compromise in cuff performance.
Many cuffs of the prior art are susceptible to partial or complete blockage of the gas passageways communicating with the tourniquet cuff. Occlusion of the gas passageways can occur in several typical scenarios, including either kinking the hose leading from the port connection, and pressing the port flange against the lower bladder surface isolating the port passageway from the bladder, either of which can inhibit the accurate sensing and regulation of pressures within the tourniquet cuff. Several anti-occlusion apparatus are described by McEwen et al. in U.S. patent application Ser. No. 11/153,667.
The manufacturing and assembly process of prior art cuffs consists of numerous cutting, sewing, and sealing operations which require substantial investment in both equipment and skilled operators. The manual labor component of cuff assembly is high, especially where multiple sewing and sealing operations are required. It is therefore desirable to reduce the skill and time required by the cuff assembly process, while continuing to utilize readily available manufacturing equipment.
A reduction in the amount of time and skill required to build a tourniquet cuff can be accomplished by reducing the number of manual assembly operations. This may include the elimination of numerous sewing operations, and the consolidation of multiple RF sealing steps into a single operation. Reducing the number of manual operations provides a savings not only in the labor to construct a cuff, but also provides the potential for the automation of a number of steps leading to the single cuff sealing operation.
In U.S. Pat. No. 6,682,547 McEwen et al. describe a method for automating the cuff manufacturing process by constructing the top layer sheet of the cuff in a continuous strip with the middle of the sheet of one thickness, tapering down at the side edges. This allows the top layer of the cuff to provide the stiffening functions described previously, while not limiting the inward radial reach of the bladder. McEwen et al. describe a custom manufacturing process which allows the bottom and top sheet material to be joined in a continuous process, whereby the edge of the inner layer is folded over the outer layer and sealed. The end edges of the cuff are sealed at various intervals to allow the construction of cuffs of a variety of lengths. The stiffened top layer therefore extends to the ends of the resulting cuff.
While manufacturing a tourniquet cuff using the design and methods described in the '547 patent may result in a high potential level of automation, the cost of creating the custom manufacturing equipment required to would be high, due to the limited similarities which exist with currently employed cuff manufacturing equipment. It is therefore desirable to use as much of possible of current cuff manufacturing infrastructure.
There is a need for tourniquet cuff apparatus which can overcome the limitations, problems and hazards of cuff performance that are described above, and for tourniquet cuff apparatus that can be manufactured using existing infrastructure, at lower cost from less materials and from inexpensive materials, with a reduced number of operations and with a reduction in the level of operator skill required.